Nutrient transport and transformation in macrotidal estuaries of the French Atlantic coast: a modeling approach using the Carbon-Generic Estuarine Model

Type Article
Date 2022-02
Language English
Author(s) Wei Xi1, Garnier Josette1, Thieu Vincent1, Passy Paul2, Le Gendre RomainORCID3, Billen Gilles1, Akopian Maia4, Laruelle Goulven GildasORCID5
Affiliation(s) 1 : UMR Metis 7619, Sorbonne Université, CNRS EPHE, 4 Place Jussieu, Paris 75005, France
2 : UMR 8586 PRODIG, Université de Paris, 8 rue Albert Einstein, 75013 Paris, France
3 : Ecosystèmes et Aquaculture Durable, Unité de Recherche Lagons, IFREMER, Nouméa 98897, New Caledonia
4 : Department of Research and Scientific Support, French Biodiversity Agency (OFB), 5 Square Félix Nadar, 94300 Vincennes, France
5 : Department of Geosciences, Environment and Society, Université Libre de Bruxelles, Brussels 1050, Belgium
Source Biogeosciences (1726-4170) (Copernicus GmbH), 2022-02 , Vol. 19 , N. 3 , P. 931-955
DOI 10.5194/bg-19-931-2022
WOS© Times Cited 6

Estuaries are key reactive ecosystems along the land–ocean aquatic continuum, with significant ecological and economic value. However, they have been facing strong morphological management changes and increased nutrient and contaminant inputs, possibly leading to ecological problems such as coastal eutrophication. Therefore, it is necessary to quantify the import and export fluxes of the estuaries, their retention capacity, and estuarine eutrophication potential. The 1-D Carbon-Generic Estuary Model (C-GEM) was used to simulate the transient hydrodynamics, transport, and biogeochemistry for estuaries with different sizes and morphologies along the French Atlantic coast during the period 2014–2016 using readily available geometric, hydraulic, and biogeochemical data. These simulations allowed us to evaluate the budgets of the main nutrients (phosphorus – P; nitrogen – N; silica – Si) and total organic carbon (TOC), and their imbalance, providing insights into their eutrophication potential. Cumulated average annual fluxes to the Atlantic coast from the seven estuaries studied were 9.6 kt P yr−1, 259 kt N yr−1, 304 kt Si yr−1, and 145 kt C yr−1. Retention rates varied depending on the estuarine residence times, ranging from 0 %–27 % and 0 %–34 % to 2 %–39 % and 8 %–96 % for total phosphorus (TP), total nitrogen (TN), dissolved silica (DSi), and TOC, respectively. Large-scale estuaries had higher retention rates than medium and small estuaries, which we interpreted in terms of estuarine residence times. As shown by the indicator of eutrophication potential (ICEP), there might be a risk of coastal eutrophication, i.e., the development of non-siliceous algae that is potentially harmful to the systems studied due to the excess TN over DSi. This study also demonstrates the ability of our model to be applied with a similar setup to several estuarine systems characterized by different sizes, geometries, and riverine loads.

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Wei Xi, Garnier Josette, Thieu Vincent, Passy Paul, Le Gendre Romain, Billen Gilles, Akopian Maia, Laruelle Goulven Gildas (2022). Nutrient transport and transformation in macrotidal estuaries of the French Atlantic coast: a modeling approach using the Carbon-Generic Estuarine Model. Biogeosciences, 19(3), 931-955. Publisher's official version : , Open Access version :